Dodge. Everything about this shark cage diving trip is dodgy as hell to Lisa (Moore). Maybe it’s that the hotel warned her not to take unlicensed tours. Maybe it’s because this was suggested to her, and her adventurous sis Kate (Holt), by two guys they met only the night before. It could be the old boat. Or the rusty cage. Or, you know, the sharks. Even the assurances of Mathew Modine’s captain don’t help, but that could be down to the beard and the bandana. Dodge. But Lisa goes ahead with it anyway because her boyfriend broke up with her for being boring. She should have listened to her gut because the cable snaps, trapping the sisters at the titular depth with air running out and sharks circling…

This mash-up of Adrift and The Shallows is an exercise in minimalism. The trim set-up, Moore and Holt aren’t asked to do more than panic, and there’s very little character development: Lisa learns to be brave is the extent of her arc. But this tidy thriller does an awful lot right with what it has with director Johannes Roberts (Storage 24, The Other Side Of The Door) having fun getting his characters into impossible situations and then finds (semi) plausible ways for them to get out of it.

The British director delights in the little jobs he gives Lisa and Kate, making each and every one as difficult as possible: although they can’t swim to the surface because of the danger of the bends, they do need to get closer so they can contact the boat. To do that they need to get the crane thing off the top of the cage so they can open the door. To do that Lisa has to squeeze through the gap. And to do that she needs to take off her oxygen mask. All the while the roaming sharks await in the darkness around them.

The dialogue is rather bland, however. When it isn’t sweating to foreshadow imminent problems – “It’ll be great!” (it won’t); “You won’t want to come back up,” (they will); “You’re only going five metres down!” (that’s just a flat out lie); and “I won’t leave you” (she will, and does) – it merely reinforces what the audience already knows: explaining what the bends are, that the oxygen is depleting rapidly, and that they’re scared. And there’s a mini twist that’s lifted big time from another British horror (and then doesn’t have the courage to follow through on it).

If youâ€™re looking for a decent shark movie this might float your cage.